Method of coating paper



p il 20, 1954 J, A. coNsTANcE 2,676,119

' METHOD OF- CUATING PAPER Fi March 15, j W 1 Patented Apr. 20, 1954 2,676,119 METHOD OF COATING PAPER Joseph A. Constance, MillersFalls, Mass., as-

signor to Brightwater Paper Company, Adams, Mass., a corporation of Delaware, and Millers Falls Paper Company, Millers Falls, Mass., a corporation of Massachusetts Application March 13, 1953,-Serial No.-342,233

readily erasable it is provided with a thin size T coating which covers both the valleys and hills of the paper surface and protects the paper substance from access by constituents of the ink which otherwise would stain it and render the writing indelible.

One important object of the present invention is to provide a method of applying the coating material by which such material may be applied to the necessary thickness uniformity in a single pass of the paper, thus materially cheapening the application of the coating which heretofore has required a plurality of surface coating treatments.

A further object is to provide a method by which the paper is exposed to the air after an initial application of the coating material has 1;

during the applications of the coating material thereto that breakage or wrinkling of the paper web is avoided.

Another object is to provide a method in which the coating material is passed in a continuous flow, and while the coating bath is maintained with a relatively narrow range of viscosity.

Further objects and advantages will appear from a further description of an embodiment of the invention as shown in the accompanying drawings in which Figure 1 is a top plan view of the coating mechanism and adjacent parts.

Figure 2 is a side elevation of the same.

Figure 3 is a longitudinal sectional view showing the drive mechanism.

Referring to the drawings, at I is shown a roll of paper in web form which is passed about a pasting drier roll 2 between the surface of this roll 2 and a continuous belt 3 which is supported on rollers 4 so arranged as to hold thepaper web against the roll 2 for a-considerable arc of its periphery. From the pasting roll the paper passes over a guide roll 5 and downwardly into a size tub or vat 6 beneath a dip roll I by which the web of paper is passed beneath thesurface o1 the sizing liquid. From this dip roll 1' the paper web passes out from the sizing liquid over an emergence roll 8 from which it again passes downwardly beneath the surface of the sizing liquid and beneath a lower rubber-coated size 7 Claims. (Cl. 117 1o3) ill) roll 9. The paper web passes upwardly around the periphery of the lower size roll 9 and through the nip between this roll 9 and an upper rubbercoated size roll ID, from which it passes over a guide roll I l and thenover the guide rolls I2. and

I3 into a suitable drier at 14.

The sizing liquid in the size tub or vat 6 is caused to flow in the general direction of the passage of the web of paper through the tub or vat. For this purpose it may be circulated as by a pump is entering into the size tank through the pipe 16 and distributor pipe 16a and flowing over a wall portion or dam ll at'the opposite end of the tub or tank into an overflow portion 18 of the tank from which it is withdrawn by the pump l5 through the pipe l9.

Bestresults have been experienced using casein or gum arabic size, preferably with a small amount of titanium oxide to whiten the coating. For the purpose of this invention, which is to apply a coating which will render the paper readily erasable, the viscosity of thesize must be kept within'rather close limits, preferably between 30 and seconds, using a M. L. pipette at F. If the viscosity is under 30 seconds, the paper produced does not properly erase because the typewriter ink penetrates into the fibers of the paper and on removal of the typewriter ink, the surface of the sheet is damaged. If the viscosity is over 35 seconds, the typewriter ink comes off the paper so easily that when erasure is attempted, or if it befiled in a crowded letter file, smudgingof the paper from the ink results.

The viscosity of the coating bath varies as the process is being carried out, sometimes increasing and sometimes decreasing so that almost constant attention is neededto maintain it Withinproper limits. 1

' The function of the emergence roll 8 is first to support the stretch of paper between the dip roll and the size roll which otherwise would sink into the bath and tend to wrinkle orbreak due to the weight of the coating flowing on top of it. This emergence roll also tends to smooth out any wrinkles which might start to form between it and the dip roll on one side andbetween it'and the size roll on the other side.- It also lifts-the paper out oi -the sizing bath and exposes itmomentarily to the air which apparently produces an incipient hardening of the surface which is found to be important in applying thedesired coating in such a manner that indelibility of the paper results. It is also important that both of the sizing rolls be positively driven and it is'also important that the variou's driving means for the paper web be driven at such relative velocities that the paper is maintained under the proper tension throughout the passage through the coating mechanism in order to avoid wrinkles in the paper and possible breakage.

The power for driving the various-rolls is derived from a driving-:motor 26 .i(sho.wnin Figure 1) which drives a continuously variable speed changer 21. This motor drives the upper size roll l through the belt 30. Fromthe upper size roll a belt drive 3| goes to the emergence roll 8 and from the emergence. roll throu h a cross belt at 32 and roll 1 isdriven; The..lower sizing roll 9 is power driven from theupper size roll through the endless chaindrive 35; the chain passing about a sprocket wheel 36 on the shaft of the upper size roll l0, partly-around a sprocket wheel 31 on the shaft of the lower size roll 9 and then around tension sprocket wheels at Hand 39 and back to the sprocket wheel 36. It is very important that both. oi. these size. rollsbe positively. driven, which is a departurefrom theusual practice where one of. the rolls .is :driven through itsfrictional contactwithathe paper. However, since. the coatingapplied renders the paper slippery, it is necessary to drive; both size rolls. in orderzthatthezpaper maybe passed through the nip withoutdisplacement of .the coating. material on the paper surfacea: Theguide rolls H and [2 are. driven. from the :change'speed mechanism 2.! inorder .thatthe papermay be maintained under the. proper tension neither. .too great nor too little, as itpassescthrough the. coating mechanism. The drierwat llwhich receives the paper after it. passes the guide roll. I 3 .isalso. positively driven and at an adjustable velocity through a. belt 4! fromr-amontinuously. variable speed changer 42 which. as. shown is drivenfrom .the lower size roll 9 through a .belt43s.

The temperature of. .the .drier; .I 4 is important, as if it istoo high .at: therstarthof. the. drying operatiornthe paper .is stickyandif it .is toohigh toward the end,.the paper..isimade. brittle. For

bestresults. the temperatureat. the entering end.

should not beabove 2755 E, but. this. temperature may'be increasedasthe drying. proceeds until at the :completiornof. the: drying operation the temperature may be :up to.'200? F..

Bythe use of the mechanism shown.herein,.the necessity for multiple. passage... .of. the paper through the coatingmechanism. has. been .elimie nated and a. satisfactory erasable. paper. pro:- cluced=inasinglepassof.the paper- The speed at whichrthe .paper maybe, passed through the drying mechanism. dependsuponthe character-of therpaper: employed -and may run from 200 to=250 feetper. minute- The. thickness of the coating may be regulated .byspacing of the size rolls which. may be. adjusted. as. is. .well knownin the art,-.;the.- driveshown permitting this.

From the' foregoing description. of the method it should: be .evident..to..those. skilled in the art that variousflchanges .and:modifications may be made without departing.fromthespirit or scope of thisinvention...

. 'I'his...application is. a...continuati0n in .part of myapplication Serial.No..152,5.27.filed March 29, 1950, now abandoned.

. Iclaim:

1'. .The. method which comprises .passing a web of paper beneath .the, surface of asizing -batha plurality .of timescbetween which thepaperis Y exposed to .the air outside of said bath and while said bath; is.;maintained at a. viscosity.- between the limits of 30 and 35 seconds using a 45 M. L. pipette at 80 R, passing the coated web through the nip between size rolls, and then drying the paper, the size being selected from the group consisting of casein and gum arabic.

2. The method-whichcomprises passing paper beneath the surface of a sizing bath'a plurality of times between which the paper is exposed to .the air outside of said bath, said bath being maintained at a viscosity between the limits 30 and 35 seconds using a 45 M. L. pipette at 80 F., passingthe paper thus coated through the nip between. aipainof. driven size rolls, and then dryingthe coated paper to a moisture content of approximately 5%" and at an initial drying temperature not exceeding 75 F., the size being selected from the. group consisting of casein and gum arabic.

3. The method which comprises passing paper beneath the surface of a sizing bath a plurality of timesbetween which the paper is exposed to the airoutside of. said bath, said bath being maintained at a viscosity between the limits 30 and 35 secondsusing a 45 M. L. pipette at 80 F., passing the. paper thus coated through the nip between a pair of driven size rolls, and then drying the coated paper to a moisture content of approximately 5% and at an initial drying temperature not exceeding.75 F. which-may be increasedto not exceeding 200 F. when the .drying has been completed, the size being selected'from the group consisting of casein and gum. arabic.

4;..The method which comprises passing paper beneath the surface of a sizing bath a plurality ofi times between which the paper is exposed to the. air outside. of said bath, said bath being maintained at a viscosity between the limits 30 andzi35 secondsusing a 45 M. L. pipette at 80 Fr, passing .the paper thus coated through the nip. between a pair. of driven size rolls, and then drying the coated paper toa moisture content of approximately 5%. and atan initial drying temperature not exceeding 75, the size being selected from'the group consisting of casein and g-umaarabic.

5:; The method .which comprises passing paper beneath the surface of a sizing batha plurality ofitimes betweenwhich the paper is exposed to the air outside of said bath, said bath being maintainedrat azviscosity between the limits 30 and 35 seconds using. a 45 M. L. pipette at 80 F., passing thezpaperthus coated through the nip between a pair'sofxldriven size rolls, and. then drying the coatedpaperxtota moisture content of approximately 5% and at an initial drying temperature notexceeding 75 which may be increased to not exceeding 200 when the drying has been completed,; the. size being selected from the group consistingofxcasein and. gum arabic..

6. The method which comprises-passing. paper beneath the surface of'a sizing bath. a plurality and seconds using a M. L. pipette at 80 F. while feeding and pressing the paper from both faces beyond its treatment in the sizing bath, and then drying the paper to a moisture content of approximately 5% at an initial drying temperature not exceeding F., the size being selected from the group consisting of casein and gum arabic.

UNITED STATES PATENTS Name Date Karcheski Apr. '7, 1874 Number Number Number 6 Name Date Sanburn Sept. 11, 1917 Callan Mar. 19, 1935 Dreyer Dec. 20, 1938 FOREIGN PATENTS ountry Date Great Britain of 1914 

1. THE METHOD WHICH COMPRISES PASSING A WEB OF PAPER BENEATH THE SURFACE OF A SIZING BATH A PLURALITY OF TIMES BETWEEN WHICH THE PAPER IS EXPOSED TO THE AIR OUTSIDE OF SAID BATH AND WHILE SAID BATH IS MAINTAINED AT A VISCOSITY BETWEEN THE LIMITS OF 30 AND 35 SECONDS USING A 45 M.L. PIPETTE AT 80* F., PASSING THE COATED WEB THROUGH THE NIP BETWEEN SIZE ROLLS, AND THEN DRYING THE PAPER, THE SIZE BEING SELECTED FROM THE GROUP CONSISTING OF CASEIN AND GUM ARABIC. 